The present invention relates to a semiconductor package applicable to integrated circuits and other semiconductor devices of the kind needing high integration and high speed operation.
Conventional semiconductor packages include one having an alumina or similar ceramic substrate, a power source and ground layer arranged in the substrate in a mesh structure, a ground layer formed on the surface of the substrate also in a mesh structure, a thin film laminate wiring formed on the surface ground layer by use of polyimide as an intermediate insulation film, and connection terminals provided on the rear of the substrate, as taught in, for example, Japanese Patent Publication No. 3-53795 and Japanese Patent Laid-Open Publication No. 4-352387. This kind of package is susceptible to leakage currents since the ground layers each have a mesh structure. This, coupled with the fact that the accuracy of characteristic impedance matching available with the package is limited, brings about waveform distortion and noise in the event of transmission of high speed signals. Moreover, the ceramic substrate has various problems relating to the process of manufacture and its structure, e.g., that it shrinks during baking, that a binder is not released, and that flatness available with grinding is limited. As a result, a ground layer having a plate structure and capable of fully shielding leakage currents cannot be implemented.
On the other hand, a printed circuit board uses a ground layer having a plate structure. However, with a printed circuit board, a wiring as high in density as the wiring of the ceramic substrate is not achievable unless a great number of through holes are formed in the circuit board. Therefore, the circuit board is no better than a mesh as to structure as well as to shielding ability. Furthermore, since the circuit board is implemented by an impregnated glass cloth, a single insulation layer has a substantial thickness and makes it difficult to reduce the distance between signal lines and the ground layer. As a result, the circuit board suffers from an increase in noise. In addition, the circuit board is basically not feasible for the transmission of high speed signals.